Nobel Peace Prize winner Wangari Maathai Wednesday called on the world to plant one billion trees as part of a global effort to fight climate change. She launched the initiative at the United Nations' Climate Change conference being held in Kenya's capital.

Maathai, who is also Kenya's assistant environment minister, told reporters that the Billion Tree Campaign that she, Prince Albert II of Monaco, and the World Agroforestry Centre are backing is a practical, hands-on way to tackle an otherwise daunting problem.

She said, "This is something that anybody can do. Anybody can dig a hole. Anybody can put a tree in the hole and water it, and everybody must make sure that the tree they plant survives. There are six billion of us and counting, so even if only one-sixth of us each planted a tree, we would definitely reach the target."

Under the Billion Tree Campaign, individuals, communities, organizations, businesses, governments, and others are encouraged to plant anywhere from one to 10 million trees.

Pledges to plant a certain number of trees are recorded on the campaign's Web site, which the United Nations Environment Program is to manage. Participants are encouraged to keep updating the Web site on their tree-planting activities so that they could be awarded with a certificate.

Trees play a vital role in the earth's ecosystem. They absorb carbon dioxide, trap rainwater and moisture, stabilize soil, control avalanches, protect coastal areas, and perform other functions.

Forests cover some 30 percent of the earth's total land area, or about four billion hectares. The Democratic Republic of Congo is Africa's most forest-rich country.

But trees are being cut down at an alarming rate. Experts say to make up for the loss of trees in the past decade, some 130 million hectares - the size of Peru - would need to be planted with some 140 billion trees over a 10-year period.

Nobel Prize winner Maathai describes the changes she has seen in her home area of Nyeri near the Aberdare forest on the slopes of Mount Kenya.

"When I was growing up, the Aberdare was a pristine forest. It was thick with indigenous trees, indigenous vegetation. There were no roads, and rivers were flowing from the mountains," she said. "Today, of course, when a child looks at the Aberdare, it's very different. Many places have been cut down. Until very recently there were large farms where people were growing food crops. And so, the Aberdare forest of today is very different from the Aberdare forest of my childhood."

And such deforestation is very worrying. The United Nations says the loss of natural forests worldwide contributes more to global emissions each year than cars and other forms of transportation.

These emissions, or so-called greenhouse gasses, form a barrier that prevents the sun's energy from radiating back into space, raising the earth's temperature. This, in turn, contributes to rising sea levels, droughts, flooding, declining crop yields, and other effects.

The Billion Tree Campaign was launched at the United Nations' Climate Change conference being held in Kenya's capital.

Some 6,000 participants are looking at the problem of climate change and what to do about it. The conference ends November 17.